1. Field of the Invention
This invention relates to an arrangement and a method for control of flow of material, particularly as applicable to an apparatus and a method for dosing the material.
2. Description of the Prior Art
U.S. Pat. No. 3,807,909 discloses a positive displacement pump for liquid or semi-liquid food products. The pump is controlled by a spool-type valve and includes a product dosing cylinder into which product is drawn and then expelled by a piston. A chamber is provided within a housing of the valve having an outlet in which is secured a nozzle having an internal chamber communicating with the remainder of the valve chamber. The nozzle chamber has upper and lower cylindrically shaped portions of given diameter separated by an intermediate section which tapers outwardly from both upper and lower portions to an expanded diameter portion at a level between the upper and lower portions. The valve spool has a lower plunger section reciprocating within the valve housing and nozzle chambers, and the plunger section has upper and lower portions matching in diameter and axial separation the respective upper and lower nozzle chamber portions. The intermediate portion of the plunger section tapers inwardly from both upper and lower plunger portions to a diameter smaller than the diameter of the upper and lower plunger portions. The piston and the spool are reciprocated in timed relationship so that, during a product intake stroke of the piston, the spool is in a lowermost position wherein both upper and lower plunger portions are positioned in sealed relationship with the upper and lower portions, respectively, of the nozzle chamber, and an upper plunger section of the valve spool is below a cylindrical inlet of the valve chamber of matching diameter while, during a discharge stroke of the piston, and when the valve spool is in its uppermost position, the upper plunger section seals in the cylindrical inlet and the upper plunger portion is positioned above the upper nozzle chamber portion, while the lower plunger portion is positioned just below the nozzle chamber upper portion, clear of the lower nozzle portion. The valve spool is initially moved upwardly from its lowermost position before the piston begins its product discharge stroke. A constricted annular opening is thereby defined through which product passes at an increased velocity to prevent air bubbles from rising upwardly in the outwardly moving product. The portion of the nozzle chamber below the lower plunger section of the valve spool provides an enlarged chamber when the valve spool is in the uppermost position, to reduce the velocity of the product as it is discharged from the nozzle into a container therebelow to minimize splashing. The valve spool includes a valve stem extending vertically from the lower plunger section to the upper plunger section and thence upwards towards a drive device. In the open condition of the inlet, its cross-section is obstructed by that valve stem and, in the open condition of the outlet, its cross-section is greatly obstructed by the lower plunger section.
WO88/06552 discloses a dosing system for filling containers with a particulate/liquid mixture and which includes three piston-and-cylinder devices, of which a first device delivers the mixture downwards to containers advanced beneath it, a second device feeds a thick particulate/liquid mixture via a conduit to the first device, and the third device feeds a thin liquid via a conduit to the first device. A liquid supply port is disposed peripherally in the cylinder of the first device, and a conduit in continuous communication with the port extends through the piston to a lower axial end of the piston. A thick mixture supply port is also disposed peripherally in the cylinder of the first device and is swept by the piston thereof. Each of the second and third devices comprises an inlet valve in the form of a rotary plug valve and a dosing piston-and-cylinder arrangement.